Complicated question and it really depends. For hunting in the old way of expecting encounters at conversational distance up to say 400-500m your game animal size has something to say about how far you should not exceed for a zero. You want to be able to hold on-hair as far out as possible and still be able to put metal right into the pumping room right? To do that you need your Point Blank Range to match your game's vital area size divided by 2 to the maximum ordinal of the bullet (bullet height above line of sight). If you set it up so you're 2.5" high at 100yrds and dead on at 250 then you're good with many rifles to somewhere around 400yrds holding on hair. I personally never liked that way of doing things, it seemed to be kinda ball-parking things with something's life on the line for my taste.
The LRH crowd though tend to look much farther for shots and that old rule of thumb goes right out the window because of how you shoot at them. We/y'all tend to identify the exact range the critter is at, dial turrets to a precise firing solution and engage from a supported position. None of those things typically gets done the way I describe in the paragraph above. So you want a dead-on zero you can rely on as a solid reference point (so your ballistics DOPE works properly) and a scope that tracks like a rolling train. Simple enough. Now we've identified that you NEED a soild reference point to dial ballistic firing solutions properly.
Some very limited military and competition circumstances have a 600m zero being right (they're only needing to put metal on meat and wound someone, not necessariliy make sure it's dead and didn't suffer) but for our ostensible purposes of long range hunting and for long range precision rifle target shooting in general I teach my students to use a 100yrd/m zero. There's a simple reason for it. It's close enough that subtle changes in things like wind, muzzle velocity and air temperature become inconsequential to getting a really solid zero and far enough to be useful. 10mph of wind is going to be 1-2 clicks and up/down changes from MV and temp are not going not going to show up at all. As you get farther out it becomes tough to tell if you've got a spurious couple inches of wind dialed in or if terrain effect is throwing off your zero.
This system of configuration and use assumes that you'll be dialing your scope to your firing solution from the middle or its mechanical range to nearly the mechanical bottom of its range for zero setting and that when normally shooting you'll be dialing up, usually a significant amount. You don't want your scope at the actual bottom of its range though for optical reasons so careful selection of bases and rings should be exercised. If you're stopping shooting at 1000yrds or somewhere closer, you're not likely going to need 100MOA of adjustment. 40 will do so you can set up the scope to be in the middle of the range for most scopes we might tend to use (they frequently have 60-80moa or more of adjustment range). On most of my guns I'm set up for going to the supersonic limits of the bullet so I tend to set up my scopes near the mechanical bottom so I have the maximum amount of up left in the scope. I don't shoot anything closer than 200m except for my zeroing target.
So to sum up, you need to take cartridge performance, game size, typical engagement range, scope adjustment range, etc... all in to account and those will generally determine for you if you MUST go further than 100yrds or if you can get away with 100yrds.
FYI, a 600yrd zero is done by shooting at 100yrds and making the POI the requisite number of mils higher than the POA. You'd never shoot for a zero at 600yrds. Wind changes would jack you up bad. So even if you're looking for a longer than 100yrd zero, there's ZERO REASON to actually shoot that zero at beyond 100 physical yards. Just adjust POI vs. POA so that the angular adjustment is there already.
If that's not insanely clear, I apologize. I tried.
